U.S. Navy SEAL Guide to Weather Secrets by Don Mann

Author:Don Mann
Language: eng
Format: epub
Publisher: Skyhorse Publishing, Inc.
Published: 2012-09-06T04:00:00+00:00

Source: Meteorology for Scientists and Engineers, 2nd Edition by Roland B. Stull

Weather Forecasting

Portable aneroid barometers, thermometers, wind meters, and hygrometers are useful in making local weather forecasts. Reports from any weather service, including USAF, USN, or the National Weather Bureau, are also helpful. But weather reports should be used in conjunction with the locally observable current condition to forecast future weather.

Remember that weather at various elevations may be quite different due to cloud height, temperature, and barometric pressure. Rainy overcast conditions may occur in a lower area, while warmer, clear weather affects the mountains.

The method a forecaster chooses will depend upon the forecaster’s experience, the amount of data available, and the level of difficulty that the forecast situation presents.

The five methods of forecasting weather are:

1. Persistence Method. The simplest way of predicting the weather assumes that “today equals tomorrow.” If today was hot and dry, the persistence method predicts that tomorrow will be the same.

2. Trends Method. “Nowcasting” involves determining the speed and direction of fronts, high- and low-pressure centers, and clouds and precipitation. For example, if a cold front moves 300 miles during a twenty-four-hour period, we can predict that it will travel 300 miles in another twenty-four hours.

3. Climatology Method. This method averages weather statistics accumulated over many years. This only works effectively when weather patterns are similar from one year to the next.

4. Analog Method. This method examines a particular day’s forecast and recalls a day in the past when the weather looked similar. This method is problematic because finding a perfect analogy is difficult.

5. Numerical Weather Prediction. This method uses computers to analyze all weather conditions and is the most accurate of the five methods.

Recording Data

An accurate observation is essential in noting trends in weather patterns. A minor shift in the winds may signal an approaching storm. Establish wind direction as a magnetic direction from which the wind is blowing. Measure wind speed in knots. Use the chart below to determine how fast the wind is blowing.

Speed

(kph) Effects of Wind

0-1 Calm. No wind; smoke rises straight up.

1-3 Light Air. Smoke moves sideways a little.

4-7 Light Breeze. Wind felt on face; leaves rustle; wind vanes move.

8-12 Gentle Breeze. Leaves and twigs in constant motion; wind moves small flags.

13-18 Moderate Breeze. Wind raises dust and loose paper; small branches move.

19-24 Fresh Breeze. Small trees begin to sway; very small waves on lakes.

25-31 Strong Breeze. Large branches in motion; telephone wires whistling.

32-38 Moderate Gale. Whole trees are in motion; hard to walk against wind.

39-46 Fresh Gale. Wind breaks twigs off trees; cannot walk in wind.

47-54 Strong Gale. Wind damages some houses; awnings blown away.

55-63 Whole Gale. Rarely experienced; trees uprooted; major damage to homes.

64-72 Storm. Lots of damage.

73+ Hurricane. Very rare; lots of damage.

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